I have to calculate possibilities like 1/10^100.

Hm. Odds that small are so close to zero as to be meaningless.

There are estimated to be 10^80 atoms in the universe. If one of them had gone missing (or an extra one had materialised into existance) at some point after matter crystallised out of the big bang, the affect the absence or presence of that one atom would have had on the form of the universe would be undetectable at any scale.

And the affect that a 1/10^100 change in probability will have (on anything) is 100 million trillion times less significant.

To try and put that into perspective. If a casino dice had 1/10^100 bias, it would undetectable by any mechanism. I would guess that every single dice ever produced has been, is, and always will be biased billions of times more significantly. A single missing electron from the face of the dice will bias it far more significantly than that.

Indeed, the bias of every dice ever made probably varies by bllions of times more than that, second by second, due to moisture absorption, evaporation or radioactive decay.

If every human being that ever existed, threw every dice that ever existed, once every microsecond, for their entire lives and you managed to record every single throw, you would not be able to detect if such a rare event had occurred or not.

So what is the point of knowing such probabilities? Even knowing that they are not zero is useless information.